This invention relates to a method of controlling the operation of a multistage hydraulic machine of the type in which flow passages of the stages are communicated with each other through return passages more particularly a controlling method effected at a time of abnormal condition which occurs when the operation of a water wheel or a pump is stopped or when the load of the water wheel is interrupted or the input of the pump is interrupted due to a fault of the machine.
In a known hydraulic machine including a pump, a water wheel or a pump turbine, the operation control of the hydraulic machine has been performed by adjusting the opening of guide vanes provided for the peripheral wall of the runners of the hydraulic machine and by adjusting the amount of the water passing through the runners.
Although, in general, a multistage hydraulic machine comprises a plurality of stages provided with runners, respectively, which are communicated with each other through return passages, a Francis-type two-stage pump turbine is illustrated in FIG. 1 as one example.
Regarding the Francis-type two-stage pump turbine shown in FIG. 1, when the water wheel is operated, the water flowing into the casing 6 through a penstock 7 is discharged into a spillway 8 through guide vanes 4, a runner 3 of a high pressure stage, guide vanes 2, and a runner 1 of a low pressure stage. On the other hand, when the machine is operated as a pump turbine the pumped-up water flows in the direction opposite to that described above.
In a case where such abnormal condition as the load interruption of the water wheel or the interruption of that pump input occurs during the operation of the water wheel or pump turbine, or where the operation thereof is stopped for an operational reason, the guide vanes are rapidly closed completely or to a slight opening. When the opening of the guide vanes is varied, the flow amount of the water is also varied thereby inducing water pressure variation in the penstock 7 due to the water hammering action caused by the variation in the flow amount of the water. Abnormally great variation of the water pressure may damage the hydraulic machine. Therefore, in order to prevent such disadvantages and to safely operate the hydraullic machine, it is necessary to control the opening of the guide vanes particularly of a multistage hydraulic machine which comprises a plurality of stages communicated with each other through a return passage.
However, since present day multistage hydraulic machines still involve many problems to be solved, a method of accurately controlling the guide vanes has been desired.
The operation of a multistage hydraulic machine will be described hereunder in conjunction with FIG. 1.
Generally, the diameter of the flow passage of the multistage hydraulic machine is a minimum at portions provided with guide vanes and therefore, the water passes the guide vanes at the highest speed. Accordingly, regarding the Francis-type multistage hydraulic machine shown in FIG. 1 in which the flow passages of the respective stages are communicated with each other through the return passage 5, when it is necessary to control the degree of openings of the guide vanes 4 and 2 having different degree of openings, the flow amount of the water is mainly affected and controlled by the guide vanes having a smaller degree of opening. As described hereinabove, when the flow amount is rapidly changed by controlling the degree of opening of the guide vanes 4, the pressure of water in the penstock 7 is caused to vary due to the water hammering action and this pressure variation propagates to the water passage of the high pressure stage communicated with the penstock. In this case, the pressure wave caused by the pressure variation in the penstock 7 is reflected mainly by the stage having the guide vanes with the minimum degree of opening and most of the reflected pressure wave propagates to the water passage located on the upstream side of the guide vanes and hardly propagates to the water passages on the downstream side thereof. Thus, the structure of the passages upstream of the guide vanes is severely affected by the reflected pressure wave, but the passage downstream thereof is not so severely affected.
Accordingly, in a multistage hydraulic machine, when it is required to rapidly control the degree of opening of the guide vanes at a time of an accident which occurs during the operation control of the machine or a time of stopping the operation, the influence of the pressure variation of the water on the flow passage of the machine, i.e. the safeness of the flow passage of the machine, will be determined by the method of controlling the guide vanes of the respective stages of the multistage hydraulic machine.